A desynchronizer is a device that recovers an embedded signal containing asynchronous data at a specific clock rate from within a higher rate digital bit stream of a synchronous channel. The clock rate for the embedded signal is unrelated to the clock rate for the synchronous channel. When the embedded signal is multiplexed into the synchronous channel, it is necessary to synchronize the embedded signal with bit or byte timing adjustments. The process of recovering the asynchronous data and clock rate of the embedded signal is complicated by data gaps and overhead timing adjustments necessary to map the embedded signal into the synchronous channel.
The conventional approach to accommodating the overhead gaps is to allow them to appear as fluctuations in the instantaneous fill level of a data buffer referred to as an elastic store. Clock recovery is accomplished by using the fill level of the elastic store to drive a low pass filter, which in turn drives a voltage control oscillator, to produce a desired clock signal for synchronous transmission of the data from the elastic store. High frequency instantaneous variations in the elastic store fill value, due to the overhead gaps installed during synchronization, are filtered by the low pass filter but not completely eliminated. Mapping jitter remains on the output of the desynchronizer due to instantaneous variations in the elastic store fill value that are not fully filtered out. Therefore, it is desirable to have a desynchronizer without any mapping jitter on its output.
From the foregoing, it may be appreciated that a need has arisen for a desynchronizer device that eliminates instantaneous variations in the elastic store fill value caused by overhead gaps on the synchronous channel. A need has also arisen to remove mapping jitter from the output of the desynchronizer device.